The Acid test: A new kind of chroma keying

SHARE THIS ARTICLE

"What is the problem with chroma key?" asked David Ross, CEO of Ross Video, at the NAB Show in Las Vegas. "When you go to a movie, do you ever say 'I can see the green edge?' No. But when you watch the weather guy pointing to a map, or a virtual set is involved, that's a different matter. What's wrong with video?"

Ross maintained that there was ‘something’ seriously amiss with current chroma key techniques – and ‘something’ had to change.

“Our goal at Ross Video is to be the leader in Virtual Solutions for all live production,” says Ross. “And right now we are introducing that change. With our set of new cameras, a whole new perspective on chroma keying is now possible.”

Called Acid, the camera range produces what Ross calls a ‘special ability to excel’ – not just where Chroma key is concerned, but a great deal more besides. And by linking Acid with the new Ross standalone chroma key system labelled as Carbonite UltrachromeHR, a high resolution key edge is generated that aims to remove the previous problems associated with virtual environments.

“We’ve developed these cameras to include a unique new signal format to overcome the difficulties of creating good chroma keys,” explains Ross. “These cameras output standard SMPTE 4:2:2 video signals for use in any production. However, in addition they output a special 0:4:4 full bandwidth colour signal that is combined with the primary output within the new Carbonite UltrachromeHR system to generate a full resolution 4:4:4 signal, perfect for developing high resolution key edges.”

We’ve ignored the problem for 25 years, so I wanted us to solve the difficulty

How it works

Ross goes on to say that the secret of the Acid success is understanding what 4:2:2 actually means “The ‘4’ is your luminance coming across – that’s the black and white. But the colour is ‘2’ and ‘2’. So, why is it when we transmit 4:2:2 we use only half the colour? Our eyes are good at black and white, but colour – you could smear it across and you won’t know the difference.”

Chroma keyers, however, do notice the difference. And with only half the colour information being available on previous systems, it is hard to determine exactly where the colour edge that needs keying starts and finishes. And that’s what causes ‘edges’ to appear.

“We’ve ignored the problem for 25 years, so I wanted us to solve the difficulty,” emphasises Ross. “What we need is 4:4:4; sampling. That sounds pretty straightforward – just fill in the colour. So how do we make that work?”

In a typical camera assembly there is a lens, a prism, and an RGB output that is converted to luminance and colour. “But then we come to the low pass filtering. That is where the difficulties arise. That is where the colour is smeared, making it almost impossible to chroma key properly.”

Acid removes the problem by including a separate output before the low pass filtering, creating a separate 0:4:4 signal. And by working with a 4:4:4 configuration, every pixel in the image in controllable. “In effect, we own every pixel,” confirms Ross. “And that means we can control the edges. On Acid cameras, edges go from fuzzy to sharp.”

He goes on, “Then there is noise. Most broadcast cameras have very acceptable signal to noise ratios. However, noise is measured in the luma channel, but chroma levels are always lower than luma values and so are inherently noisier. That noise ends up in the chroma key edges unless it is filtered out – which lowers the edge resolution even further. With our system, edges are blended properly and you get better transparencies, as well.”

Key to success

But in order to create keys from this new signal, it was obvious that an innovative chroma keyer design was also needed.

It’s at that stage that the companion to Acid is introduced – Carbonite UltrachromeHR.

Ross continues, “This enables high resolution Chroma keying. This is a carbonite black that is turned into a high end two or four channel high-end keyer. But how high-end? Not only does it do 4:4:4, but it also has three keyers which is important for background/foreground keying for sophisticated virtual sets in augmented reality.”

UltrachromeHR also provides eight media stores for the extra video that is available, and 16 frames of variable input delay.

“All of this means we don’t have to sell you as much open gear to solve those delay problems,” admits Ross.

The system includes two multiviewers, enabling operators to tweak and fine-tune the numerous signals that are now possible to generate.

“That means you can control as many Chroma keyers as you need on one customised screen.” Ross adds that the Carbonite UltrachromeHR is also the world’s first 4K Chroma keyer. “So we have an ideal pair. A 4:4:4 camera and a 4:4:4 keyer – perfect.”

Most broadcast cameras have very acceptable signal to noise ratios. However, noise is measured in the luma channel, but chroma levels are always lower than luma values and so are inherently noisier

Two options

Currently, two Acid options are available. The Acid H200 is a full HD 1080P, three imager camera that utilises the latest 2/3” UAIT CMOS sensors to provide high quality output. Sensitivity, signal-to-noise and overall picture resolution are, claims Ross, unmatched by any competitor with its three 2.6 Mega Pixel image sensors and standard 2/3” B4 lens mount. “Plus, it has all the features you’d expect to find on any high end studio camera,” states Ross.

For moderate budgets and less critical applications, there is the Acid Z50. This is a three CCD sensor 1080i/720P HD camera.

Like all Ross products, Acid cameras embrace DashBoard control. All camera operation, setup and shading can be performed from DashBoard panels including the transfer and recall of scene files from one Acid camera to another.

Ross explains more, “What DashBoard does here is replace the CCU and gives access to every single control in the camera in real time. It eliminates the need for costly CCU for a great many customers. And it is customisable. It doesn’t matter whether you have four, six, eight or more cameras, control is there. And if you just want to ride the blacks, you can create a panel within DashBoard that does just that.

He concludes, “Acid cameras are game changers and Ross is the company who is changing the game. However, even if you don’t use chroma keys, Ross Acid cameras produce spectacular video images in normal studio production. With this exciting new product introduction Ross now offers a complete video production solution from capture to final output. Acid cameras not only produce spectacular video images in normal studio production, but they turn virtual production into compelling virtual reality.”